Polyacetal resins have high mechanical strength and rigidity, have high oil resistance, organic solvent resistance, and self lubrication, and have a good balance among properties in a wide temperature range.
The polyacetal resins are easy to process, and used as typical engineering plastics in a wide range including mechanical parts and sliding parts for precision instruments, home appliances, OA apparatuses, automobiles, and industrial materials and articles.
Particularly, it is known that the polyacetal copolymer has a comonomer component more chemically stable than the polyacetal homopolymer; accordingly, decomposition does not continuously progress even if the chain is cut in the middle thereof, providing high heat aging resistance, hydrolysis resistance, and molding stability.
Recently, the polyacetal resin has been used in a broader application field, leading to higher performance to be demanded.
In such circumstances above, in order to enhance designability of molded articles in addition to the various physical properties, attempts have been made to improve appearance properties and give a metallic gloss to the molded articles.
For example, a method for producing a molded article has been proposed in which the surface of a difficult-to-adhere resin is subjected to a blasting treatment, and a metallic film is formed on the surface of the resin by vacuum evaporation (for example, see Patent Document 1.).
Moreover, as a coating material to be applied to a molded article formed of a polyacetal resin in order to improve the appearance, a metallic pigment dispersion comprising a flake-like metallic pigment having an extremely small content of a product by a fatty acid reaction or decomposition and a binder or a binder solution has been proposed (for example, see Patent Document 2.).
Further, a powder coating material composition comprising a thermosetting resin powder having a flake-like pigment bonded to the surface thereof has been proposed (for example, see Patent Document 3.).
Moreover, attempts have been made to demonstrate a metallic gloss by molding a resin containing a gloss pigment and give designability. For example, a metallic pigment having a specific particle size and shape ratio (thickness/particle size ratio) and added to a synthetic resin composition and a resin molded product containing the metallic pigment have been proposed (for example, see Patent Documents 4 and 5.).
Further, methods have been proposed such as a method in which a predetermined amount of a metallic pigment and a predetermined amount of a colorant which can optically change are contained in a thermoplastic resin; a method in which a gloss pigment to be added to a resin and comprising a specific aluminum particle is contained (for example, see Patent Documents 6 and 7.); and a method in which a weather proofing agent, a formaldehyde inhibitor, and a metallic pigment are added to a polyacetal resin having a specific terminal structure (for example, see Patent Document 8.), and suppression in the amount of formaldehyde to be produced and improvement in the weatherability are shown as the effects.
Moreover, a composition has been proposed in which a polyacetal copolymer contains a weather proofing agent, an aluminum particle having a specific particle size, particle size distribution, and particle thickness, and a specific fatty acid, and production stability, mechanical physical properties, molding appearance, weld performance, and lightness are high (for example, see Patent Document 9.).
Further, as improvement of an aluminum pigment, in addition to improvement in the particle size and shape ratio (thickness/particle size ratio), a technique has been proposed in which the surface roughness of the aluminum particle is focused, and high luminance and high flop properties are given (for example, see Patent Document 10.).